1. Field of the Invention
The present invention relates to a false twisting air nozzle employed for fasciated yarn spinning, and more particularly to such an air nozzle having a fiber bundle passage including an inlet, a smaller-diameter hole portion, and a larger-diameter hole portion arranged in the order named from an upstream end to a downstream end thereof in the direction of travel of a bundle of fibers, there being at least one air injection port opening tangentially in the downstream direction in the larger-diameter hole portion of the fiber bundle passage.
2. Description of the Prior Art
Ring spinning has been employed for many years to produce spun yarns composed of short fibers. Due to the low production rate, however, the ring spinning is being replaced with new spinning methods capable of producing spun yarns at higher rates of production. Such new spinning methods include open-end spinning, self-twist spinning etc. These spinning methods still have disadvantages. For example, the open-end spinning process fails to achieve spinning operation at much higher speeds as the process requires a heavy rotor to be rotated, and has a problem in spinning thin yarns of the yarn count 40 and over. Although the self-twist spinning can produce spun yarns at high speeds, it is subjected to a limitation on the length of fibers it can handle, and is restricted to spinning of two folded yarns.
To solve the shortcomings with the foregoing spinning processes, there has been proposed fasciated yarn spinning which is based on the principle of high-speed yarn twisting effected by false twisting. According to the fasciated yarn spinning, a flat ribbon of fibers that has been supplied from a drafting device is twisted and untwisted by a false twisting nozzle to produce a fasciated spun yarn. The fasciated yarn spinning method utilizes, as a main component, an air false twisting nozzle which is required, as shown in FIG. 1 of the accompanying drawings, both to draw a bundle of fibers fed out by front rollers F into the nozzle and to turn the fiber bundle to twist and untwist the same. The former function serves the purpose of introducing the fiber bundle into the nozzle, and the latter function serves the purpose of binding together the fiber bundle. The former function is also important in preventing the fibers from being wound on the front rollers F and waste cotton from being produced.
As illustrated in FIG. 1, the conventional false twisting nozzle comprises an inlet 1 progressively spreading toward a fiber bundle supply end (to the left as shown), a smaller-diameter hole portion 2 and a larger-diameter hole portion 3 which are contiguous to the inlet 1. Air injection holes 4 have ends opening in the larger-diameter hole portion tangentially in a downstream direction (to the right as shown). Another prior nozzle comprises, a shown in FIG. 2, a fiber bundle passage having a smaller-diameter hole portion 2 and a larger-diameter hole portion 3 interconnected by a connecting portion 5 in which an end of an air injection hole 4 opens.
The force with which the fiber bundle is drawn into the nozzle can be produced by a stream of air injected from the air injection hole 4 into the nozzle, and is affected by various factors such for example as the diameters of the hole portions 2 and 3, the angle at which the latter spreads downstream, and the angle of inclination of the air injection hole 4. In particular, the fiber sucking force is greatly influenced by the smaller-diameter hole portion 2 in that the smaller the diameter of the hole portion 2, the smaller the fiber sucking force becomes. It is therefore effective in increasing the fiber sucking force to enlarge the diameter of the smaller-diameter hole portion 2. With the increased diameter of the hole portion 2, however, the fiber bundle as it is rotated by the air stream undergoes accelerated ballooning and hence is not fed along stably, with the results that the resultant yarn will have varied yarn strengths or be caused to break off in extreme cases. The diameter of the smaller-diameter hole portion 2 of the conventional nozzle is reduced to a size small enough to suppress such yarn ballooning. This prevents the fiber suction force from being sufficiently great, resulting in troubles such as the production of fly or waste cotton due to an air stream caused by high-speed rotation of the fiber bundle supply unit and the winding of fibers onto the fibers bundle supply unit.